Cause of nephrocalcinosis in granulomatous ds –
Correct Answer: Increased conversion to 1,25 OH
Description: <p>In patients with sarcoidosis and other granulomatous diseases, such as tuberculosis and fungal infections, excess 1,25(OH) 2 D is synthesized in macrophages or other cells in the granulomas.Indeed, increased 1,25(OH) 2 D levels have been repoed in anephric patients with sarcoidosis and hypercalcemia. Macrophages obtained from granulomatous tissue conve 25(OH)D to 1,25(OH) 2 D at an increased rate. There is a positive correlation in patients with sarcoidosis between 25(OH)D levels (reflecting vitamin D intake) and the circulating concentrations of 1,25(OH) 2 D, whereas normally there is no increase in 1,25(OH) 2 D with increasing 25(OH) D levels due to multiple feedback controls on renal 1a-hydroxylase . The usual regulation of active metabolite production by calcium and phosphate or by PTH does not operate in these patients. Clearance of 1,25(OH) 2 D from blood may be decreased in sarcoidosis as well. PTH levels are usually low and 1,25(OH) 2 D levels are elevated, but primary hyperparathyroidism and sarcoidosis may coexist in some patients.(harrison 18 pg 3108)</p>
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